1. Technical Field
The invention relates to secondary suspension systems for trucks and, more particularly, to a truck cab suspension system providing noise and shock isolation through an inexpensive, compact and simple mechanism.
2. Description of the Problem
The load carried by a truck is supported by a frame which is resiliently carried by suspension springs from the truck's axles. The primary axle suspension springs usually have very high spring rates which make the ride jarring to the operator and to structures such as a cab supported by the frame. It is desirable to isolate vehicle cabs and their occupants from shock and vibration. Doing so enhances cab occupant comfort and extends the service life of the cab by reducing stress to the cab. Stress promotes structural damage, particularly to spot welds used in assembly of the cab structure.
To dampen the vibration and shock transmitted to the cab, secondary suspension systems have been employed utilizing conventional suspension components such as air springs to isolate the cab structure from shock and shock absorbers to dampen motion of the cab, respectively. A wide variety of cab suspensions exists in the art. A typical configuration includes hard rubber mounts at the front end of the cab and a combination of an air spring and shock absorbers installed along a rear sill of the cab. The front mounting elements are required to absorb longitudinal loads transmitted between cab and frame. The rear suspension elements provide shock isolation and damping of vertical motion. Frequently the cab structure in the cab floor area and the front mount area is beefed up to take the stress. Rear impact plates to take the stress of the suspension elements are also known. Frame beaming contributes considerable vertical loading into the cab when rubber mounts for the cab are placed on beaming anti-nodes. The anti-node in many heavy truck applications is at the back of cab location.